This invention relates to fluid support systems and is concerned with, (but is not to be considered as being restricted to), fluid support systems for supporting, at least in part, the bodies of persons confined to bed.
When a person is confined to bed, soft tissue is compressed between the skeleton and the supporting surface. Care is usually taken to provide a deformable mattress but, nevertheless, high local pressures occurring in the deformed tissue will compress blood vessels and tissue damage may result. A patient resting on a normal hospital bed will experience local pressures of the order of 150 mm Hg (2.9 psi). The blood pressure through the capillary vessels of the skin and underlying tissue is generally accepted as being 26 mm Hg (0.503 psi), but this figure may be considerably reduced for an ill patient. When contact pressures exceed this value, blood flow is stopped, resulting in transient damage and, finally, deep penetrating necrosis of tissue, muscle and bone. Skin may also be damaged by shear stresses resulting from friction between the skin and the supporting structure. Such stresses are a function of the local pressure and the area of contact.
At least some of the aspects of the present invention can be viewed as improvements in the fluid support system disclosed by my U.S. Pat. No. 4,279,044.